In many parts of the world, rainfall is insufficient and/or too irregular to keep turf and other landscape vegetation green and therefore irrigation systems are installed. Such systems typically include a plurality of underground pipes connected to sprinklers and valves, the latter being controlled by an electronic irrigation controller. One of the most popular types of sprinklers is a pop-up rotor-type sprinkler. In this type of sprinkler a tubular riser is normally retracted into an outer cylindrical case by a coil spring. The case is buried in the ground and when pressurized water is fed to the sprinkler the riser extends. A turbine and a gear train reduction are mounted in the riser for rotating a nozzle turret at the top of the riser. The gear train reduction is often encased in its own housing that is commonly referred to as a gear box. A reversing mechanism is also normally mounted in the riser along with an arc adjustment mechanism.
The gear drive of a typical rotor-type sprinkler can include a series of staggered gears and shafts wherein a small gear on the top of the turbine shaft drives a large gear on the lower end of an adjacent second shaft. Another small gear on the top of the second shaft drives a large gear on the lower end of a third shaft, and so on. Alternatively, the gear drive can comprise a planetary arrangement in which a central shaft carries a sun gear that simultaneously drives several planetary gears on rotating circular partitions or stages that transmit reduced speed rotary motion to a succession of similar rotating stages. The planetary gears of the stages engage corresponding ring gears formed on the inner surface of the housing. See, for example, U.S. Pat. No. 5,662,545 granted to Zimmerman et al.
Two basic types of reversing mechanisms have been employed in commercial rotor-type sprinklers. In one design a reversing stator switches water jets that alternately drive the turbine from opposite sides to reverse the rotation of the turbine and the gear drive. See for example, U.S. Pat. No. 4,625,914 granted to Sexton et al. The reversing stator design typically employs a long metal shaft that can twist relative to components rigidly mounted on the shaft and therefore this arrangement undesirably changes the reversal points. Stopping the rotation of the stator and changing direction of rotation via alternate water jets does not provide for repeatable precise arc limits. In addition, persons that manually set the arc of rotor-type sprinklers that employ a reversing stator design do not get a tactile feel for a stop at the set arc limits.
A more popular design for the reversing mechanism of a rotor-type sprinkler includes four pinion gears meshed together and mounted between arc-shaped upper and lower frames that rock back and forth with the aid of Omega-shaped over-center springs. One of the inner pinion gears is driven by the gear train reduction. The pinion gears on opposite ends of the frames alternately engage a bull gear assembly to rotate the nozzle back and forth between pre-set arc limits. The arc limits are effectuated by a shift dog alternately engaging an adjustable arc tab and a fixed arc tab. See for example, U.S. Pat. Nos. 3,107,056; 4,568,024; 4,624,412; 4,718,605; and 4,948,052, all granted to Edwin J. Hunter, the founder of Hunter Industries, Inc., the assignee of the subject application. While the reversing frame design has been enormously successful, it is not without its own shortcomings. It involves a complicated assembly with many parts that can have operational failures. The main drawback of the reversing frame design is that the pinion gears are held in contact to the outer bull gear with a spring force that is relatively weak. Therefore, high speed torque forces which are sometimes generated in this type of sprinkler can cause the reversing frame gears to slip out of engagement or wear out.
At some irrigation sites it is important to utilize a sprinkler that can be set so that its nozzle oscillates between selected arc limits, or in the alternative, set so that its nozzle will rotate continuously to provide three hundred and sixty degrees of coverage. U.S. Pat. No. 7,861,948 of Crooks discloses a rotor-type sprinkler having a reversing frame design that allows adjustable arc selection or in the alternative, full circle mode operation to be selected. While this rotor-type sprinkler has experienced considerable commercial success, its reversing mechanism is not suitable for a more robust rotor-type sprinkler with a planetary gear drive of the type disclosed in the aforementioned U.S. Pat. No. 7,677,469.